Heat treatment of oil or the like stored on a water-bed in a storing container



Sept. 13, 1955 H. EDHOLM HEAT TREATMENT OF OIL OR THE LIKE STORED ON A WATER-BED IN A STORING CONTAINER 5 Sheets-Sheet 1 Filed July 25, 1950 INVENTOR. HARALD EDHOLM ATTORNEYS.

Sept. 13, 1955 H. EDHOLM 2,717,719

HEAT TREATMENT OF OIL OR THE LIKE STORED ON WATER-BED IN A STORING CONTAINER Filed July 25, 1950 5 Sheets-Sheet 2 INVENTOR HARALD EDHOLM ATTORNEYS.

P 13, 1955 H. EDHOLM 2,717,719

HEAT TREATMENT OF OIL OR THE LIKE STORED ON A WATER-BED IN A STORING CONTAINER Filed July 25, 1950 5 Sheets-Sheet C5 Fig/ Hg. 5

INVENTOR. HARALD EDHOLM in m,

ATTO R NEYS Sept. 13, 1955 H. EDHOLM 2,717,719

HEAT TREATMENT OF OIL OR THE LIKE STORED ON A WATER-BED IN A STORING CONTAINER Filed July 25, 1950 5 Sheets-Sheet 5 HARALD EDHOLM dam, m;

ATTORNEYS.

United States Patent HEAT TREATMENT OF 01L OR THE LIKE STORED ()N A WATER-BED DJ A STGRENG CONTAINER Harald Edholm, Solsidan, Saltsjobaden, Sweden Application .luly 25, 195%, Serial No. 175,841

16 Claims. (Cl. 222-1) The present invention relates to the heat treatment of oil or the like stored on a water-bed in a storing container.

In the storing of viscous oil or the like provisions should be made for heating the oil, in some instances during the storing period in order to demulsify as far as possible water contained in the oil, and particularly in connection with the tapping of the oil for the purpose of facilitating transport of the oil in pipe lines. In case the oil stored and the temperature of the oil has dropped during the storing period below the pouring temperature, heating is indispensable.

When ordinary steel plate cisterns or tanks are used, from which the oil is taken out near the bottom of the tank, the oil is generally heated by means of coiled pipes positioned in the lower portion of the container and sometin es also in a separate heating chamber near the oil outlet.

When storing oil on a water-bed, a storing method which is of interest particularly in blasted-out rock chamhers below the ground Water level, the upper oil surface is preferably kept at an approximately constant level in the upper part of the container. When oil is taken out from the upper part of the container, water is simultaneously filled into the lower part thereof, or vice Versa. The level of the lower oil surface in contact with the water-bed is thus dependent on the amount of oil stored at the moment.

It is a primary object of the present invention to secure the lowest possible installation and operating costs for the heating of the oil. According to the invention the said object has been attained by heating the oil column by means of heat supplied mainly to the lower portion of the oil column.

According to one embodiment of the invention the heat is supplied mainly indirectly through the intermediary of the water-bed. In this manner'the advantage is obtained inter alia, that the heat will spread uniformly through the entire upper boundary layer of the waterbed, resulting in a uniformly distributed heating of the entire bottom layer of the oil column. In this case the solidified oil is thus melted over the entire cross section of the container, and no solidified oil can remain at the Walls of the container when raising the water-bed.

Fartioularly the thick fuel oils produce a sediment of asphalt-like heavier substances in admixture with emulsified water which originates from the refinery or has entered the oil during the sea transport or during the time of storing in the oil container. Said sediment is the cause of great inconveniences, since it cannot be utilized as fuel oil but must be taken out separately from time to time as a waste product of only a slight or no value. Similar difficulties are encountered also in connection with the storing of certain vegetable and animal oils or fats.

If the sediment is heated to a high temperature, for

example 50 C. to 80 C., the sediment becomes highly liquid. The emulsification of the water is thereby facilinas high solidifying and pouring temperatures tated, and the strong heat circulation set up in the oil results in that the sediment, at any rate a great portion thereof, becomes mixed again with the overlying oil so that it can be taken out and utilized together with the latter.

To secure the best possible heat economy it is, however, desirable that the heating should be restricted, in accordance with the invention, to the upper layer only of the water-bed. Such a hot water layer in the upper part of the water-bed will remain for a long time and will transmit its heat mainly to the overlying oil through circulation but only to a small extent to the underlying cold parts of the water-bed through heat conductance.

The supply or heat to the water-bed can be effected according to the invention either through exchange of heat between a heating unit positioned in the water-bed and the water in the water-bed, or else by supplying artificially heated water to the water-bed while simultaneously, if required, removing a corresponding amount of cold water from the lower part of the water-bed. The last mentioned alternative entails the advantages of simple arrangements in the container proper and high safety of operation.

in order to be able at all to take out the molten oil from the lower part of the oil column in a container containing solidified oil, it is, however, necessary to heat the oil within a vertical column-shaped zone extending through the entire solidified oil column up to the oil pump in the upper part of the container. According to the invention this object is attained by providing heat emitting units of suitable type in a Zone extending through the entire oil column. if heating is effected by means of an electric heating unit submerged in the water-bed, said unit thus must be combined with extra heating means extending up through the oil column. If the heating is effected by means of hot water or a steam battery in the water-bed, the more or less heat insulated supply pipes to said heaters may be utilized as extra heating means.

According to another alternative embodiment of the invention heat is supplied to the oil directly in that the lower part of the oil column, which is raised and lowered together with the Water-bed, is kept in contact with heating members placed in the oil proper. Also in this case it may, however, be advantageous, according to the invention, to heat the oil also higher up in the oil column. T his is the case, for instance, if the stored oil is solidified or viscous, in which case oil can be tapped on short notice from the upper part of the oil column only if heat is supplied to the oil throughout the entire height of the oil column up to the oil out-take.

An arrangement according to the invention for realizing the above mentioned method consists substantially of one or more heating and/or hot water emitting members placed in the water-bed or oil column respectively.

The invention will now be described more in detail with reference to the accompanying drawings.

On the drawings:

Figures 1 to 7 show different embodiments of the arrangement according to the invention.

Figure 7a is a diagrammatic representation of the conditions prevailing in the arrangement shown in Figure 7.

Figures 8a and 8b illustrate in section and partly diagrammatically the conditions prevailing in an embodiment of a heating arrangement according to the invention.

Figures 9 to 14 illustrate in vertical section further different embodiments of the invention, Figures 11:: and 1111 being cross sections along the lines XIa--XIa and Xlb-Xlb respectively in Figure 11.

Figure 15 shows on an enlarged scale a particular embodiment of the heating arrangement.

In the embodiment shown in Figure l a container 1 contains, between the levels 2 and 3, a column of solidified oil resting on a water-bed extending between the levels 3 and 4. Oil can be filled into the container and be taken out therefrom through a pipe associated with a pump 5 in the upper part of the container. Cold water can be filled in and taken out through a water pipe 6, which reaches down to the bottom of the container. A heating unit 8 is placed at the bottom of the container and heats the water-bed substantially above the dotted line 9, resulting in that the oil is gradually melted in the lower part within a zone which is limited on top by the dotted line 10. The heat supply pipe 7 of the heating unit melts out in the oil a vertical column-shaped zone having its boundary surface at 11, through which zone the molten oil can be taken out if simultaneously cold water is supplied to the bottom of the container through the pipe line 6. If oil is not immediately taken out heat will be transported to higher levels on account of the heat movements in the bottom layer of the oil, resulting in that the molten layer successively grows, so that the boundary surfaces represented by the lines and ll. move upwardly and outwardly respectively.

Figure 2 shows the modification that there is provided instead of the heating unit a hot water emitting unit con sisting of a supply pipe 7 and a cup-shaped guide member 12, which directs the stream of water upwardly. If oil shall not be taken out immediately, an amount of cold water corresponding to the amount of hot water introduced can be taken out simultaneously from the lower portion of the water-bed through the pipe 6. In the two embodiments according to Figures 1 and 2 comparatively much heat or hot water for heating the water-bed is consumed. The said embodiments are therefore economical in the first instance when small temperature rises and treatments of larger amounts of oil at a time are concerned.

Figure 3 shows an improved arrangement consisting of a plurality of heat or hot water emitters l2 placed one above the other and preferably adapted to be raised and lowered somewhat, each emitter having its own supply pipe. Only that emitter, which is positioned in the waterbed nearest to the oil layer, should be kept in operation.

Figure 4 shows a heating unit 8 suspended in the supply pipe 7. The heating unit, which is adapted to be raised and lowered, is always kept in the upper part of the water-bed, whereby a hot water layer 14 is formed immediately below the oil level 3. The raising of the heating unit can be effected, for example, by successively removing pieces of the supply pipe at 15, or by making the supply pipe above the container in the form of a flexible hose or a telescopic pipe.

Figure 5 shows the modification that the heating unit has been replaced by a hot water emitting member consisting of the supply pipe 7 and a guide plate 16 which deflects the hot water horizontally towards all sides. Tests made have shown that it is possible, without any heat losses worth mentioning, to spread out the hot water in a thin layer below the oil. The arrangement is also suitable when it is desired repeatedly to treat and take out small amounts of oil at a high temperature.

Figure 6 shows two modifications of the arrangement of the supply pipe, one modification being drawn with dotted lines showing a fixedly mounted pipe 7 and a flexible hose 18, the other one being drawn in full lines and comprising a fixedly mounted pipe 19 and a turnable pipe 20. The hot water emitter 8 can be raised and lowered by means of a wire 21.

The embodiments according to Figures 4 and 6 thus require, that the supply pipe for the heat or hot water emitters is movable or adjustable with respect to its length to render possible the raising and lowering of the same according as the level of the water-bed is changed.

According to Figure 7 an emitter 12 for hot water is placed at the bottom of the container and is surrounded by a perforated tube 22, which with its upper part reaches up through the upper part of the container and which preferably also encloses the supply pipe 7 leading to the emitter. In this manner the hot water may be transported through the tube up to the level 2 of the oil without mixing too much with the surrounding cold water. This will be clearly understood from Figure 7a, which iliustrates a tight tube 22 extending up to a level near the water surface 3 and enclosing a supply pipe 7 for hot water. In the diagram according to Figure 7a the ordinate shows the height h in meter, reckoned from the upper end of the tube, and the abscissa p the corresponding pressure in meter water column. The quantity p hxy is the pressure of the cold water against the outside of the tube wall 22, and the quantity p,,=h.' is the pressure of the lighter hot water against the inside of the tube wall, 'y and designating the specific weights of the cold and the hot water respectively. The static overpressure on the outside of the tube is thus ,,=P '-P1,-= 1'Y2) When the hot water flows through the tube, there occurs a pressure loss [7 :h.p where p designates the pressure loss per meter length of tube. If now the dimensions of the tube and the velocity of hot water are so chosen that p =A i. e. p =1(Y 'y the pressure at each point inside the tube wall will be the same as that outside of the wall, wherefore theoretically the conditions of flow would not be changed if the tube were perforated. The conditions of flow are, however, unstable. In practice, it is therefore not possible to obtain the ideal condition of iiow, but tests have shown that it is actually possible to transport, through a perforated tube according to the invention, the greater part of the hot water up through the cold water zone of the water-bed, although with a rather considerable temperature reduction on account of mixedin cold water.

It is, however, possible, according to a further development of the invention, to improve said method, for instance by providing on the outside of the tube cover piates which extend down over the apertures or slits provided in the perforated tube. Said cover plates form Within the cold water zone of the water-bed together with the tube liquid seals which resist the inflow of cold water into the tube or the outflow of hot water from the tube, provided that the dimensions of the tube and the velocity of fiow of the hot water are chosen in a suitable manner. This will be clear from Figures 8a and 8b, which show two sections through the tube 22, one section being taken at the upper warm part of the water-bed and the other one further down within the cold water zone. The tube 22 is provided with horizontal slits 23 and with cover plates 24, which together with the wall of the tube form cold water seals within the cold water zone, Figure 8b, provided that the velocity of the water is so chosen that the pressure within the tube is somewhat, e. g. the quantity p, higher than the outside pressure, thus P +P =P +P' If the pressures within and outside of the tube were alike, i. e. p p =p the boundary layer between the hot and the cold water would be on a level with the slit 23, and a small pressure reduction in the tube would cause cold water to flow into the tube. On account of the additional pressure p the boundary layer is, however, pressed down to the level 26. Only if the additional pressure p is increased to a quantity p, corresponding to a lowering of the boundary layer to the level 27, the hot water will start to flow out of the tube. Compare the diagram according to Figure 8b, where the abscissa p designates the pressure and the ordinate the height on the same scale as that of the tube 22. The water seal thus counteracts the exchange of water in both directions. Within the hot zone in the uppermost part of the water-bed, Figure 8a, the conditions are otherwise. Since, after the starting period, the temperature of the Water in said zone will be substantially the same at both sides of the tube the water seal will not function, wherefore the hot water can flow out through the slit without any other hinderance than the frictional resistance. Compare the diagram in Figure 8a, where p designates the water pressure inside of the tube and p the water pressure outside of the tube. The difference p ,p,,,=p then represents the just men tioned frictional resistance only.

The result will thus be-and this has been verified by tests-that by means of the said arrangement hot water can be transported without any exchange losses worth mentioning from the bottom of the container through the cold water zone up to the upper surface of the waterbed and be spread out there. This will take place wholly automatically, independently of the position of the waterbed in the container.

Figure 9 shows a general drawing of such a plant. The tube consists of a number of preferably heat insulated tube lengths 22 which are widened at their lower ends and are pushed over each other so that horizontal slits 25 are formed which function within the cold water zone as water seals. Within the oil zone the oil will be heated not only in the bottom layer but also in the space between the hot water pipe 7 and the tube lengths 22. The tube lengths 22, which may be heat insulated, delay the heating of the oil around the tube, wherefore it is possible, each time oil is to be taken out, to take out in the main only the bottom layer. In this manner the formation of a bottom layer of thicker products is prevented.

The arrangement shown in Figure 9 requires for its normal functioning, as already mentioned, a certain definite velocity of the hot water. When forced heating is desired it may be suitable, in view of the dimensions of the tube, to use a higher hot water velocity. This is possible if the tube lengths 22 are made displaceable with respect to each other, so that the perforations can be closed within the cold water zone and be kept open only within the zone next below the surface of the water-bed and possibly also within the oil zone or within the lower part of the latter. Such an embodiment is shown in Figure 16, where a number of heat insulated tube lengths 22, which are coupled together by means of spacer links 26, are suspended in a lifting member 27 so as to form together a perforated tube which on being successively lowered towards a fixed support 28 at the bottom of the container is pushed together, so that, starting from the bottom, the tube lengths form a more or less tight tube within the cold water zone of the water-bed. This embodiment does not require any complicated arrangements and is readily adjustable during operation. In Figure 10 the tube is, for the sake of clearness, shown with considerably exaggerated dimensions as regards diameter and links. The tube lengths may, if desired, be provided with cover plates forming water seals as in Figure 9, and also in this case they may, as indicated in connection with Figure 9, be adjusted for full automatic functioning. Alternatively, the tube link system may, of course, be fixedly suspended at the upper part of the container and be raised successively in the lower part. In such a case the supply pipe 7 and the emitter 12 must be adapted to be raised and lowered, however.

Figure ll shows another embodiment comprising an adjustable tube 22, which is tight within the cold water zone. Said tube consists of two perforated mutually turnable pipes Zfi and 30, one of which is provided with a straight longitudinal slit 31 and the other one with a spiral-shaped slit 32, said pipes being adapted to be set in such mutual turning positions that the composite tube becomes more or less tight within the cold water zone of the water-bed. At the point of intersection 33 of the slits a free opening for water or oil respectively is formed.

This embodiment may be modified so that the two perforated pipes are mutually displaceable in their longitudinal directions instead.

The perforation of the tubes referred to above may be made in many different ways, with a system of slits or apertures, provided only that the object set forth is obtained, viz. that a free connection between the inside of the tubes and the surrounding medium is formed only at the desired level.

In certain cases it may be desirable to make the tube so that its cross section is increased upwardly or downwardly.

The formation and arrangement of a hot Water layer the upper part of the water-bed is highly facilitated if the specific weight of the hot water layer can be further reduced with respect to the specific weight of the water in the rest of the water-bed. This is possible in cases when the oil is stored on salt-water. In such a case it is advantageous to supply the hot water in the form of fresh water. The difference in specific weight can be about doubled by said measure.

In Figure the container is shown as containing for the moment oil 1W2 between the levels 103 and 104. The oil rests on the water-bed 105. The boundary layer between water and oil is designated with 103. Water can be introduced or removed through the pipe 6. Provided in the container is a heating unit 107 which is adapted to be raised and lowered and which has the supply and return pipes 13%. According to the invention the heating unit is lowered to the lower part of the oil column. The pipes 119, Figure 12, may preferably be arranged to emit heat to the oil. The embodiment is suitable in the first instance in cases where only smaller amounts of heat are to be supplied to the oil, in that in such cases the heating unit can be made with small weight and can be adapted to be raised and lowered in a simple manner.

figure 13 shows another embodiment of the invention comprising a fixedly mounted heating member. The said member is made in several sections 107 to 111, in the example shown in the form of a spirally bent pipe, each section having its own supply pipe 112.

'igure 13 shows the sections coupled together. According to the invention the sections may, however, alternatively be entirely separate from each other with a separate supply pipe for each section; compare Figure 14. In Figure 13 the sections 107, 108 and 109 are for the moment in contact with the oil. Heating may be eifected with only the lowermost or with several of the said sections coupled in. If the heating of the oil is effected by means of a through-flowing heating medium, said medium may move in either direction. The sections can be so arranged that in a horizontal plane the heat is concentrated to a certain part of the cross section of the container or else is distributed over a larger or smaller part thereof. It may be suitable to position the pipe coils in the same horizontal plane at different distances from the centre to provide for better heat distribution.

Figure 14 shows a modification of the last mentioned embodiment which is suitable for oils which do not solidify at the natural temperature in a non-heated underground containcr. The heating means are here positioned only in the upper part of the container. The heating means are shown as divided into sections 115, 107 and 163, but can also consist of a single section. The purpose of the heating member is to render it possible to heat the last portion of the oil in the container and to facilitate the emulsification of Water, and the concentration of the sediment to the boundary surface 163 before the oil is taken out. The heating members may be used for heating of the oil also when the waterbed occupies lower levels than in Figure 14.

The heating means can be made either according to Figures 13 and 14 in the form of pipe spirals or in the form of horizontal rings or the like.

if the oil is so viscous or has so high a solidifying point that separate heating arrangements are required in connection with its storing, the oil is transported and filled into the container in a heated condition. In ordinary overground steel plate cisterns or tanks the oil will cool down after a short time. To keep the oil warm during an extended period of time would be too costly. It is cheaper to heat the oil anew when it is to be taken out. The heating then has to be made in a short time with a high effect, which in connection with larger containers requires a large boiler plant, for instance of the order of magnitude of one or more hundreds of square meter heating surface, and large heat-emitting surfaces on the heating members in the container.

In underground containers, on the other hand, where the oil is in direct contact with rock walls the heat losses are very small as compared with the heat losses in freelying cisterns. According to the present invention it is suitable approximately to compensate for the comparatively small heat losses in the rock containers or cisterns by supplying small amounts of heat during the storing time, thereby maintaining or adjusting the oil temperature to a value suitable for treatment of the oil or at 1" any rate to keep the oil in a molten condition. For said purpose there is required for large containers a boiler plant of only a few tenths of square meters of heating surface and comparatively small heating units in the container. Said method results in a very considerable saving in installation costs and thus also in a corresponding saving in the fixed yearly costs for the heating of the oil, a saving which outweighs several times the additional costs for keeping the oil in rock containers permanently warm during the storing period instead of heating the same only when oil is to be taken out. The higher storing temperature also provides the advantages that the settling of water and sediment is accelerated and that the oil is always ready for delivery.

The last mentioned method can be utilized with the aid of the arrangements according to Figures 12 to 14. Figure 15, however, shows an arrangement which is more suitable for keeping the oil warm over a long period of time. The heating members 1197 to 111 are here so placed that they will surround a Zone extending from the centre of the container and out to an imaginary curtain which extends substantially along the walls of the container and which divides the container vertically into a central preferably larger part 137 and an outer part 118, which contains a more or less thick oil layer along the walls of the container. The exchange of heat with the surroundings will take place substantially through convection currents within the outer layer 113, thus between the heating members 197 to 16) and the walls of the container, whereas the oil in the central part it)? on the whole will lie still and remain at a rather constant temperature, which facilitates settling of water and sediment.

It would seem to be most suitable to secure the pipe coils 107 to 111 to the rock wall, but this manner of erection actually entails considerable costs in view of the necessity of providing scaffolding et cetera for the erection work. It has been found to be much more simple and less costly to suspend, according to the present invention, the pipe coils in the upper part of the container by means of vertical supporting members in the form of wire ropes, connecting rods or the like.

If the solidifying or pouring point of the oil is higher than the temperature of the walls of the container, the heat losses and thus also the amount of heat to be supplied may be reduced further by permitting a solidified or viscous oil layer 116 to form along the walls of the container, preferably along the side walls thereof.

Finally it is within the area of the invention to keep the section or sections of the heating member, which are positioned in the boundary zone comprising the lower part of the oil column and the upper part of the waterbed, connected-in for heating both the oil and the water within the boundary Zone. The heated water spreads out in a uniformly warm layer below the entire boundary surface of the oil and heats the latter or prevents its cooling. Furthermore, the solidified oil which may have collected on the walls of the container is melted.

In ordinary oil containers there will collect at the bottom water emulsified in oil, sediment, and asphaltlike or resinous substances. Said components form at the bottom a mushy mass, which is difficult to pump. Said mass must therefore be removed manually by shovelling, the system having thereunder to be taken out of operation for a comparatively long time. Admixed in said mass are considerable amounts of oil which cannot be utilized but go to waste. In containers having a water-bed said sediment will collect in the lower part of the oil column above the water-bed. By keeping the lower part of the oil column heated according to the invention, possibly during the entire storing time, the settling of said impurities to a more concentrated sediment immediately above the water-bed is facilitated. When the greater part of the oil has been taken out it is suitable to raise the temperature of the oil further by means of the heating section 115 provided in the upper part of the container, possibly also by means of the sections 107 and 108. After the greater part of the oil has been removed said concentrated sediment will collect in the upper, preferably restricted part of the container and may readily be removed after all oil in the upper part of the sediment layer has been taken out.

I claim:

1. A method of withdrawing oil from containers in which an oil column rests on a water layer having a variable upper level, comprising the steps of supplying heat to the upper portion of said water layer adjacent to the oil while leaving the lower portion of said water layer unheated, thereby effecting heating of at least a portion of the oil, withdrawing liquid oil from the oil container, and supplying water to the water layer so as to vary the upper level thereof.

2. A method of withdrawing oil from containers in which an oil column rests on a water layer having a variable upper level, comprising the steps of supplying heat to the oil column to raise the temperature of at least a portion of said oil column while leaving at least the main portion of the water layer unheated, withdrawing oil, and supplying water of lower temperature than the heated oil to the water layer so as to vary the level thereof.

3. A method of withdrawing oil from a container in which a column of oil rests on a water layer having a variable upper level, comprising the steps of heating at least a portion of the oil column while it is resting on the water layer, drawing heated oil from the upper portion of the oil column and raising the interface between oil and water by supplying to the lower portion of the container Water of a temperature which is lower than that of the heated oil.

4. A method of withdrawing oil from containers in which an oil column rests on a water layer having a variable upper level, comprising the steps of supplying heat to the upper portion of said water layer adjacent to the oil While leaving the lower portion of said water layer unheated, thereby effecting heating of at least a portion of the oil, withdrawing liquid oil from the oil container, and supplying water to the water layer at the lower portion thereof so as to vary the upper level thereof.

5. A method of withdrawing oil from containers in which an oil column rests on a water layer having a variable upper level, comprising the steps of supplying heat to the oil column to raise the temperature of at least a portion of said oil column while leaving at least the main portion of the water layer unheated, withdrawing oil, and supplying water of lower temperature than the heated oil to the water layer at the lower portion thereof so as to vary the level thereof.

6. A method of withdrawing oil from containers in which an oil column rests on a water layer having a variable upper level, comprising the steps of supplying hot water to the upper portion of said water layer adjacent to the oil while leaving the lower portion of said water layer unheated, thereby effecting heating of at least a portion of the oil, withdrawing liquid oil from the oil container, and supplying water to the water layer so as to vary the upper level thereof.

7. The method of heating oil having a specific gravity less than that of water in a container having a water layer in the bottom thereof on which said oil floats, comprising heating said water and oil adjacent to the interface of the oil and water while leaving at least the lower portion of said water layer substantially unheated.

8. A method as defined in claim 7 in which the heat is applied below said interface.

9. A method as defined in claim 7 in which the heat is applied above said interface.

10. A method as defined in claim 7 in which the heat is supplied by the introduction of hot water.

11. An apparatus for heating oil having a specific gravity less than that of water, in a container having a water layer in the bottom thereof on which said oil floats, comprising means for the introduction of heat adjacent to the interface of the oil and water and means for supplying water to said water layer at a point remote from that of the introduction of heat to provide control of the level of said interface.

12. An apparatus as defined in claim 11 in which said first means includes a line for supplying hot water.

13. An apparatus as defined in claim 11 in which the position of said first means may be varied within the container.

14. An apparatus for heating oil having a specific gravity less than that of water, in a container having a water layer in the bottom thereof on which said oil floats, comprising means for supplying heat to at least a portion of said oil, means for shutting off said supply of heat from at least the lower portion of said water layer, and means for supplying water to said water layer at a point remote from that of the introduction of heat to provide control of the level of said interface.

15. Apparatus as defined in claim 14 in which said first means includes a line for supplying hot water.

16. An apparatus as defined in claim 14 in which the position of said first means may be varied within the container.

References Cited in the file of this patent UNITED STATES PATENTS 103,823 Archer June 7, 1870 143,810 Cowell Oct. 21, 1873 872,561 Fess Dec. 3, 1907 1,516,343 Knight Nov. 18, 1924 1,883,021 Silknitter Oct. 18, 1932 1,929,231 Yirava Oct. 3, 1933 2,337,472 Kares Dec. 21, 1943 

1. A METHOD OF WITHDRAWING OIL FROM CONTAINERS IN WHICH AN OIL COLUMN RESTS ON A WATER LAYER HAVING A VARIABLE UPPER LEVEL, COMPRISING THE STEPS OF SUPPLYING HEAT TO THE UPPER PORTION OF SAID WATER LAYER ADJACENT TO THE OIL WHILE LEAVING THE LOWER PORTION OF SAID WATER LAYER UNHEATED, THEREBY EFFECTING HEATING OF AT LEAST A PORTION OF THE OIL, WITHDRAWING LIQUID OIL FROM THE OIL CONTAINER, AND SUPPLYING WATER TO THE WATER LAYER SO AS TO VARY THE UPPER LEVEL THEREOF. 